1. Field of the Invention
The invention relates, in general, to flash memory devices and, more particularly, to a method of manufacturing a flash memory device, in which a contact hole of a square shape is formed through a dual mask process of a line fashion employing a hard mask layer, thus improving a bridge occurring between contacts.
2. Discussion of Related Art
In the formation method of the drain contact hole of a flash memory device, if an exposure process using ArF having a low wavelength as a light source in order to form micro patterns of 70 nm or less is performed using a photoresist (PR), Contact Edge Roughness (CER) of the patterns is degraded. Accordingly, spacer margin between patterns is reduced when the micro patterns are formed, causing a bridge between the patterns.
More particularly, since the space width between the contact holes on the layout is small, the etch selectivity is lowered when the drain contact hole is formed. Areas between the contacts are attached and thus collapse, thereby generating a bridge between the contacts.
During the process of forming an elliptical drain contact hole, if the size of the contact hole is set small in order to secure a space width between the contact holes due to the characteristic of the exposure process, the size of the contact hole in a long-axis direction is increased to reduce bridge margin between a drain select line (DSL) and a drain select line (DSL). It reduces the size of the contact hole and thus makes it difficult to secure the bridge margin between the contacts.
The occurrence of the bridge between the drain contacts results in global column FAILURE. Accordingly, the loss of the yield, which is incurred by one drain contact bridge, is very high.